Process for the preparation of microcapsules

Abstract

The invention relates to a process for the preparation of microcapsules having a capsule wall of polyurea and encapsulating a water-immiscible pesticide. The process comprises first dispersing a solution of a polyisocyanate in the sparingly water-soluble pesticide, in the presence of an anionic dispersant and at least one nonionic protective colloid and/or a nonionic surfactant, and subsequently reacting the dispersion with a polyamine, to give a stable aqueous suspension of microcapsules which can be used either direct or after dilution with water as pesticidal composition.

What is claimed is: 
     
       1. In a process for the preparation of an aqueous suspension of microcapsules having a capsule wall of polyurea and encapsulating a water-immiscible pesticide, by dispersing a solution of a polyisocyanate in the sparingly water-soluble pesticide in water and subsequently reacting the dispersion with a polyamine, the improvement which comprises effecting the dispersion of the solution of the polyisocyanate in the sparingly water soluble pesticide in water and the subsequent reaction of the dispersion with the polyamine in the presence of an effective viscosity-reducing amount of (a) an anionic dispersant selected from the group consisting of a salt of polystyrenesulfonic acid, a salt of polyvinylsulfonic acid, a salt of a condensate of naphthalenesulfonic acid and formaldehyde, a salt of a condensate of naphthalenesulfonic acid with phenolsulfonic acid and formaldehyde, and a salt of ligninsulfonic acid, and (b) at least one nonionic protective colloid or nonionic surfactant or both. 
     
     
       2. A process according to claim 1, which comprises the use of an anionic dispersant which is a salt of polystyrenesulfonic acid, a salt of a condensate of naphthalenesulfonic acid with formaldehyde or a salt of a condensate of naphthalenesulfonic acid with phenolsulfonic acid and formaldehyde. 
     
     
       3. A process according to claim 1, which comprises the use of an anionic dispersant which is a salt of a condensate of naphthalenesulfonic acid with phenolsulfonic acid and formaldehyde. 
     
     
       4. A process according to claim 1, which comprises the use of a nonionic protective colloid which is a water-soluble polymer with a molecular weight of 10,000 to 200,000. 
     
     
       5. A process according to claim 3, which comprises the use of a nonionic protective colloid which is a polymer selected from the group consisting of polyvinyl alcohol, polyvinyl methyl ether, polyvinylpyrrolidone, hydroxyethyl cellulose, hydroxypropyl cellulose, methyl cellulose, hydroxyethyl cellulose, hydroxypropylmethyl cellulose, poly(2-hydroxyethyl)methacrylate, poly[2-(2-hydroxyethoxy)ethyl)methacrylate, polyethylene oxide and polyallyl alcohol. 
     
     
       6. A process according to claim 4, wherein polyvinyl alcohol is used as nonionic protective colloid. 
     
     
       7. A process according to claim 5, which comprises the use of a nonionic protective colloid which is a polyvinyl alcohol with a viscosity of 4-60 cp (measured in 4% aqueous solutions at 20° C.) and which has been prepared by saponifying polyvinyl acetate to a degree of saponification of 80-95%. 
     
     
       8. A process of claim 1, which comprises the use of a nonionic surfactant which is an ethylene oxide/propylene oxide block polymer or is a product obtained by reaction of ethylene oxide, or by combined reaction of ethylene oxide and propylene oxide, with a substance selected from the group consisting of fatty alcohols, alkylphenols, fatty acids, fatty acid esters of polyhydroxy compounds, fatty acid amides and fatty amines. 
     
     
       9. A process according to claim 8, which comprises the use of a nonionic surfactant which is an ethylene oxide/propylene oxide block polymer, a N,N,N',N'-tetra(polyethoxypolypropoxyethyl)ethylenediamine, a nonylphenol polyglycol ether, an ethoxylated fatty alcohol or an ethoxylated fatty amine. 
     
     
       10. A process according to claim 8, which comprises the use of a nonionic surfactant which is an ethylene oxide/propylene oxide block polymer. 
     
     
       11. A process according to claim 1, which comprises using a polyisocyanate selected from the group consisting of tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, toluylene diisocyanate, diphenylmethane-4,4'-diisocyanate, polymethylene polyphenylisocyanate, 2,4,4'-diphenyl ether triisocyanate, 3,3'-dimethyl-4,4'-diphenyl diisocyanate, 3,3'-dimethoxy-4,4'-diphenyl diisocyanate, 1,5-naphthylene diisocyanate, 4,4',4"-triphenylmethane triisocyanate and isophorone diisocyante. 
     
     
       12. A process according to claim 11, which comprises using diphenylmethane-4,4'-diisocyanate or polymethylenepolyphenylisocyanate. 
     
     
       13. A process according to claim 1, which comprises using a polyamine selected from the group consisting of ethylenediamine, propylene-1,3-diamine, tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, 4,9-dioxadodecane-1,12-diamine, 1,3-phenylenediamine, 2,4-toluylenediamine, 4,4'-diaminodiphenylmethane, 1,5-diaminonaphthalene, 1,3,5-triaminobenzene, 2,4,6-triaminotoluene, 1,3,6-triaminonaphthalene, 2,4,4'-triaminodiphenyl ether, 3,4,5-triamino-1,2,4-triazole, and 1,4,5,8-tetraaminoanthraquinone. 
     
     
       14. A process according to claim 13, wherein hexamethylenediamine is used. 
     
     
       15. A process according to claim 1, which comprises using a pesticide selected from the group consisting of haloacetanilides, triazole derivatives, carbamates, phosphoric acid esters, and dihydro-1,3-thiazol-2-ylidine anilines. 
     
     
       16. A process according to claim 1, wherein the process is carried out in the temperature range from 10°-75° C. 
     
     
       17. A process according to claim 16, wherein the process is carried out in the temperature range from 20°-45° C. 
     
     
       18. A process according to claim 1, wherein the components required to form the capsule walls are employed in an amount of 2.5 to 30% by weight, based on the material to be encapsulated. 
     
     
       19. A process according to claim 18, wherein the components required to form the capsule walls are employed in an amount of 5 to 20%, based on the material to be encapsulated. 
     
     
       20. A process according to claim 1, which comprises using in addition to the amounts of anionic dispersant and nonionic protective colloid and/or nonionic surfactant an amount of water sufficient to form a suspension of microcapsules which contains 100 to 700 g of microcapsules per liter. 
     
     
       21. A process according to claim 20, which comprises using in addition to the amounts of anionic dispersant and nonionic protective colloid and/or nonionic surfactant an amount of water sufficient to form a suspension of microcapsules which contains 400 to 600 g of microcapsules per liter.